The sealing of pipe joints and other leak locations in pipes and pipelines is a critical concern, and proper sealing has become more important as efforts have increased to protect the environment. Liquid chemicals, sewage, toxic gases, and other fluid-like materials such as fine dust, must be conducted through pipelines without leakage of the material from the pipeline and without contamination from outside the pipeline. To seal pipe joints, pipeline installers typically encircle the joint with a cylindrical coupling consisting of either two semicylindrical pieces fastened together to clamp the pipe ends, or a single cylindrical piece having an axial split which allows the coupling to be open by an amount sufficient to fit over the pipe ends.
Annular gasket members, such as O-rings, may be placed around the pipe ends beneath the coupling to block the escape of fluid between the coupling and pipe ends, but it is also necessary to block escape of fluid outwardly through the axial split of the coupling. Several prior devices for this purpose have been developed, as described in U.S. Pat. Nos. 4,360,227; 1,607,943; 2,913,262; 3,153,550; 4,664,428; and 5,086,809, and U.S. patent application Ser. Nos. 07/978,770 filed Nov. 19, 1992, entitled "Pipe Coupling with Sealing Plate" and 07/861,940 filed Apr. 2, 1991, entitled "Sealing Plate for a Pipe Coupling".
For example, U.S. Pat. No. 4,664,428 discloses a sealing plate for preventing passage of fluid from between the annular gasket members of a pipe coupling to the outer surface of the pipe coupling through the axial split of the pipe coupling. One sealing plate disclosed in this patent fits over the annular gasket members and between the coupling and the pipe ends and spans the axial split. The sealing plate includes axial gaskets on opposing edges for preventing the flow of fluid to the outside of the coupling. The coupling is closed by closing plates or flanges mounted to the pipe coupling on each side of the axial split. The closing plates are fastened by bolts extending through holes in the closure plates. The holes in the closure plates are larger in diameter than the bolts so that the bolts may be inserted into the closure plates while the closure plates are still apart and at an angle to one another.
When a pipe coupling such as that disclosed in U.S. Pat. No. 4,664,428 is mounted to a pipe or pipeline containing pressurized fluid, the pressurized fluid exerts forces on the coupling. The resultant forces act on the coupling to pull the closure plates in opposite directions and away from one another. If the pressure in the pipe or the pipeline exceeds a particular level, the section modulus of the coupling is overcome and the spaces between the bolts and the bolt holes in the closure plates allow the closure plates to rotate which causes a lifting of the body of the coupling up and off of the associated pipe or pipeline. As a result, the pressure of the coupling on the annular gasket members is reduced and the annular gasket members can be extruded through the space between the coupling and the pipe. This can result in a leak. It is not a practical solution to make the bolt holes smaller. If the bolts connecting the closure plates were to fit more tightly in the bolt holes, the insulation of a coupling would be too difficult.
Therefore, there is a need for a pipe coupling of the type having an axial split that can withstand higher pressures without failing.